PREPARATION OF MICROCAPSULES

The invention relates to a complex coacervation process based on the use of type B gelatin as polycationic colloid, for the preparation of "Halal" certified flavor-containing microcapsules.

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PREPARATION OF MICROCAPSULES
Technical Field
The present invention relates to the food and flavor industry. It concerns more
particularly a complex coacervation process for the preparation of flavor-containing
microcapsules which can be "Halal" certified. The process of the invention is based on the
use of a type B gelatin as positively charged polymeric wall material.
Background Art
Coacervation also called aqueous phase separation, is a very well known technique
for encapsulating hydrophobic liquids. A coacervation process allows to provide oil-
containing microcapsules, the encapsulating material being a gelled hydrophilic colloid
that is impervious to the oil and deposited evenly and densely about the oil as nucleus. The
encapsulating material is a protein which may be complexed with another colloid having
an opposite electric charge.
A coacervation process essentially involves an aqueous protein solution which is
manipulated by changing the physico-chemical environment (dilution and/or adjustment of
pH) to result in phase separation of the protein from the solution to varying degrees
depending on the molecular weight of the protein, its isoelectric point and compatibility
with solvents.
A coacervation process may be "simple" or "complex". The former designation is
employed when a single protein is used to form a capsule wall as phase separation is taking
place. The latter term designates the use of a second oppositely charged non-protein
polymer to bring about phase separation. Complex coacervation method is widely
practiced in commercial processes and has been well described in the literature. In
particular US 2,800,457 and US 2,800,458 disclose complex coacervation in a very
detailed manner.
Generally, a coacervation process comprises four basic steps consisting of,
respectively, emulsification, coacervation, wall formation and wall hardening. In a
complex coacervation process the wall surrounding the re material is, as mentioned
above, constituted of two oppositely charged high molecular weight colloids. In most of
the cases, the positively charged colloid used is a gelatin, a functional protein derived from
collagen by hydrolysis and subsequent extraction. There are two commercially available
food/pharmaceutical grade gelatins, designated respectively as "type A gelatin" and "type
B gelatin". The primary difference between the two grades, arises from the manufacturing
process. If the collagen source is hydrolyzed bv an acid, the final product gets a
designation "A" and if it is done by a liming (base) it is desienated "B'. From a product
standpoint, the two gelatins differ primarily in their isoelectric points. Type A gelatin has
an isoelectric point comprised between 8.5 to 9.0 while type B gelatin has an isoelectric
point varying from 4.8 to 5.5. In a process such as coacervation that predominantly
depends on the eletrokinetic stability of the system, such difference in isoelectric points
can be critical for a successful encapsulation.
The prior art related to complex coacervation almost always describe the use of
type A gelatin as a canonic protein wall. The pH during a process involving a type A
gelatin is kept to values inferior to the isoelectric point of the latter in order to have it
positively charged. Some documents from the prior art mention the possibility to use also
gelatin provided by basic hydrolysis (type B) as a cationic protein wall, but to our
knowledge, no example has ever really described such an embodiment and it has been
established that the processes disclosed in the prior art do not allow the preparation of
satisfactory microcapsules when type B gelatin is used as protein wall, in. its cationic form.
On the other hand, type B gelatin is sometimes mentioned in complex coacervation
processes of the prior art as being used as polyanionic polymer i.e. in its electronegative
form, in combination with a type A gelatin as positively charged colloid.
Now, as with many food ingredients, there are some regulatory constraints on
gelatin uses, from a religious/ethnic standpoint. This includes "Kosher" and "Halal" status
of gelatin. Generally, type A gelatin manufacturing process uses pig skin as starting
material. As a consequence the microcapsules produced from this starting product cannot
receive the "Halal" or "Kosher" status. Type B gelatin, on the other hand, issued from cows
or fishes, could receive either Halal or Kosher certification. However, no complex
coacervation process disclosed in the prior art to date technically allows the preparation of
microcapsules based on type B gelatin.
Now, we have been able to establish a novel coacervation process suitable for the
preparation of microcapsules based on type B gelatin as cationic wall material.
Varaporn Buraphacheep Junyaprasert ct al. describe in Drug Development and
Industrial Pharmacy, 27(6), 561-566 (2001), a complex coacervation process for the
encapsulation of Vitamin A, which uses type B gelatin in combination with gum acacia as
wall materials. However, the process parameters there-disclosed are not optimized, in
particular, the drug contents of the microcapsules do not exceed 50% w/w.
The process according to the present invention allows to overcome the drawbacks
observed in the prior art by providing an optimized complex coacervation process suitable
for the preparation of microcapsules susceptible of being "Halal" certified, and containing
up to 80% w/w of hydrophobic core material.
Disclosure of Invention
The invention relates to a novel complex coacervation process, specially suitable
for the preparation of high fix microcapsules encapsulating a hydrophobic core material,
such microcapsules being susceptible of being incorporated into "Halal" certified foods or
flavors. The process of the invention uses type B gelatin as polycationic colloid, in
combination with a polyanionic material. The process parameters, such as pH, or the order
of the processing steps, are critical for a successful encapsulation. More particularly, the
process is characterized by the fact that the pH is adjusted before the emulsification or
dispersion step, to a value between 3.0 and 4.7.
The invention also relates to the microcapsules that are produced by this process.
These microcapsules can be "Halal" certified and they comprise up to 30% by weight of
hydrophobic core material.
The invention also relates to a method for imparting, improving or modifying the
organoleptic properties of a food composition, wherein microcapsules prepared by the
process of the invention, are added to said composition, as well as food compositions
comprising said microcapsules as an active ingredient
A first object of the present invention is therefore a process for the preparation of
hydrophobic core material-containing microcapsules, which process comprises, in this
order, the steps of: a) mixing solutions of a positively charged high molecular weight
colloid and a negatively charged high molecular weight colloid; b) adjusting the pH of the
mixture obtained under a) to a value comprised between 3.0 and 4.7; c) emulsifying or
dispersing a hydrophobic core material in the mixture; d) subjecting the emulsion or
dispersion obtained under c) to water dilution and/or pH adjustment to achieve
coacervation; e) cooling the coacervate obtained under d) to provide wall formation of
microcapsules ; and f) adding a hardening agent; said process being characterized by the
fact that the positively charged high molecular weight colloid is a type B gelatin.
What is meant by "high molecular weight" is typically a molecular weight
comprised between 40 000 and 100 000.
The terms "hydrophobic core material" encompass hydrophobic liquid materials
which are usually subjected to encapsulation by coacervation, as well as solids or solids
suspended in a hydrophobic liquid.
Although some documents from the prior art cite type B gelatin as a possible
starting material for a complex coacervation process, it turned out that the disclosed
processes cannot in fact allow to produce satisfactory microcapsules based on this wall
forming material, unless type B gelatin is in its anionic form. Now, the process of the
invention allows the preparation of very efficient delivery systems based on the use of type
B gelatin in its cationic form, which systems present the advantage of containing a very
high load of hydrophobic core material and on the other hand of being in accordance with
religious/ethnic regulatory constraints. More objects, aspects and advantages of the
invention will become apparent from the detailed description, as well, as in the example
below.
In the first step of the process according to the invention, soluions of, on the one
hand, a positively charged high molecular weight colloid, and on the other hand, a
negatively charged high molecular weight colloid, are mixed together. The process is
characterized by the fact that the positively charged high molecular weight colloid is a type
B gelatin. The use of type B gelatin in its cationic form is very unusual in this type of
process. It implies that the pH of the solution is set to a value below its isoelectric point i.e.
below 4.8-5.5.
As mentioned above, type B gelatin is obtained from basic hydrolysis of a collagen
source (e.g. from cow or fish). The base catalyzed hydrolysis takes several days to be
completed. Details of the process are well known by a skilled person in the art.
As the negatively charged colloid, any anionic polymer that reacts with the protein
to form complex coacervates will suit the process of the invention. In particular gum
arabic, sodium alginate, agar, carrageenan, carboxymethyl cellulose, sodium polyacrylate
or polyphosphoric acid are suitable anionic polymers for the purpose of the invention.
In a particular embodiment, the ratio between gelatin and the oppositely charged
colloid is of 3 :2.
Step b) of the process of the invention consists in adjusting the pH of the mixture
obtained under step a) to a value comprised between 3.0 and 4.7. This can be typically
achieved by means of addition of lactic acid. This step is essential in the process of the
invention, in terms of specific pH values, as well as from a process stage point of view. In
fact, the adjustment is operated before the addition of the hydrophobic core material,
contrary to what is disclosed in the processes of the prior art, wherein the pH is usually
adjusted after emulsification or dispersion step. Now, in an unexpected manner, it turned
out that the adjustment of the pH to a suitable value at this particular stage of the process,
is responsible for an efficient wall formation of the microcapsules.
Once the pH is adjusted, a hydrophobic core material is emulsified or dispersed in
the mixture. As mentioned above, this core material may consist of a hydrophobic liquid,
as well as of a solid or yet a solid dispersed in a hydrophobic liquid.
In a particular embodiment of the invention, the core material to be encapsulated is
a liquid flavor ingredient or composition. These terms can define a variety of flavor
materials of both natural and synthetic origin, currently used for the preparation of food
compositions. They include single compounds or mixtures. Specific examples of such
components may be found in the current literature, e.g. in Fenaroli's Handbook of Flavor
Ingredients, 1975, CRC Press ; Synthetic Food Adjuncts, 1947 by MB. Jacobs, edited by
Van Nostrand; or Perfume and Flavor Chemicals by S. Arctander 1969, Montclair, N.J.
(USA). These substances are well known to the person skilled in the art of flavoring and/or
aromatizing consumer products, i.e. of imparting a flavor or taste to a consumer product
traditionally flavored, or of modifying the taste of said consumer product.
Natural extracts can also be encapsulated into the system of the invention; these
include e.g. citrus extracts such as lemon, orange, lime, grapefruit or mandarin oils, or
coffee, tea, mint, cocoa, vanilla, or essentials oils of herbs or spices, amongst other.
The proportion of hydrophobic core material is comprised between 35 and 90% by
weight relative to the weight of gelatin used.
The process of the invention is of course also suitable for the encapsulation of other
core materials than flavoring ingredients, such as perfuming ingredients, Pharmaceuticals
or cosmetic ingredients.
The following steps of the process are respectively coacervation by water dilution
and/or pH adjustment, followed by the cooling of the coacervate to provide wall-formation.
The cooling must allow to reach a temperature where the colloids do gel. In a particular
embodiment, the cooling rate is comprised between 0.25 and 0.5°C/min.
Finally, a hardening agent is added in order to cross-link the wall formed around
the hydrophobic core material. Typical examples of hardening agents suitable for the
purpose of the invention include formaldehyde, acetaldehyde, glyoxal, glutaraldehyde,
chrome alum and the like.
Microcapsules susceptible of being obtained by a process according to the
invention constitute another object of the invention. These delivery systems present the
advantage of being potentially "Halal" certified, and can therefore be used for the flavoring
of so-designated final consumer products.
On the other hand, the microcapsules of the invention are very highly loaded in
hydrophobic core material. More particularly, the microcapsules may contain up to 80% by
weight of a hydrophobic core material, while the processes disclosed in the prior art only
allowed to have up to 35% by weight of active ingredient in the capsules.
The final products have a wall thickness and a morphology very satisfactory and
comparable to that of microcapsules prepared starting from type A gelatin at same fix
level, as revealed by microscopic pictures shown in figures 1 and 2.
The microcapsules produced by the process of the invention can be used in many
kinds of applications in the field of foods and flavors. Therefore, food compositions
comprising the microcapsules according to the invention together with other flavoring
coingredients, are also objects of the present invention.
accompanying
Brief Description of accompanying Drawings
Figures 1 and 2 (Fig.1 and 2) are microscopic pictures at 10x magnification of
complex coacervates prepared respectively with type A (Fig. 1) and type B (Fig. 2) gelatin
as cationic polymers.
Modes of Carrying out the Invention
The invention will now be described in a more detailed manner in the example
below, wherein the temperatures are indicated in degrees Celsius and the abbreviations
have the usual meaning in the art.
Example 1
Preparation of microcapsules according to the process of the invention - comparison with
other processes
Type B gelatin (250 Bloom, origin: SKW Biosystems, USA), gum arabic, cold pressed
orange peel oil, limonene, eugenol, and octyl acetate were used for the preparation of
microcapsules. Several trials were made, varying the concentrations of colloids, the pH of
the system, the amount of dilution water, the order of the process steps and the ratio
between gelatin and gum arabic.
Table 1 reports the amounts of ingredients used in each trial.
Table 1 : Amounts of gelatin, water, sum arabic, water, flavor and dilution water in the
process of the invention in five trials
Trial # 1 2 3 4 5
Gelatin [g] 9- 9 7.5 9 9
Water [g] 100 100 10C 100 100
Gum arabic [g] 6 6 7.5 6 6
Water [g] 150 150 150 150 150
Flavor [g] 60 60 60 60 60
Dilution water [g] 200 400 400 200 200
Procedure for preparation
All the microcapsules were prepared by a process comprising the basic steps of
emulsification or dispersion, coacervation (water dilution), wall-focming (cooling) and
cross-Unking. However, from one trial to another, the proportions of ingredients and/or the
stage of pH adjustment in the process were changed. In all the trials, the colloid solutions
were mixed at a temperature of 37-40°. The final temperature of the system was 22-24°.
The pH was adjusted by addition of lactic acid. The cooling rate was comprised between
0.25 and 0.5°/min. After cooling the batch to the final temperature, 0.14% by weight of
glutaraldehyde solution (25%) were added to cross-link the protein wall.
Trial #1 : Components were mixed in the following order : the flavor (cold pressed orange
peel oil) was emulsified in a mixture of gelatin solution and gum arabic solution. Dilution
water was added. The batch pH was then adjusted from 4.64 to 2.82 in decrements but
there was practically no wall formation.
Trial #2 : The trial was identical to trial 1, except for doubling the amount of dilution
water. Trial was unsuccessful.
Trial #3 : Identical to trial #2 except that the concentrations of the colloid solutions were
changed along with the ratio. Trial was unsuccessful.
Trials #1to 3 demonstrate the essential character of the order in which the steps of the
process of the invention are performed. When the pH is adjusted after the
emulsification/dispersion step, no wall formation occurs.
Trial #4 : Identical to trial #1 in formulation. Order of addition was changed. After mixing
the colloid solutions, pH was adjusted to 3.0 with lactic acid, prior to the addition of flavor
oil. Excellent wall formation was observable. This trial proves the importance of the pH
adjustment' stage in the process.
Trial #5 : Everything was done like in trial #4, except that the flavor consisted of a 60 : 20 :
20 mixture of limonene, eugenol and octyl acetate. Trial was successful.
It can be concluded from the above experiments that the preparation of microcapsules with
type B gelatin is successful as long as the pH of the colloid solution is suitably adjusted
and as long as this is done prior to the addition of the hydrophobic core material.
WE CLAIM;
1. A process for the preparation of hydrophobic core material-containing
microcapsules, which process comprises, in this order, the steps of:
a) mixing solutions of a positively charged high molecular weight colloid and a negatively
charged high molecular weight colloid having a molecular weight between 40,000 and
100,000 ;
b) adjusting the pH of the mixture obtained under a) to a value comprised between 3.0 and
4.7;
c) emulsifying or dispersing a hydrophobic core material, such as herein described, in the
mixture;
d) subjecting the emulsion or dispersion obtained under c) to water dilution and/or pH
adjustment to achieve coacervation ;
e) cooling the coacervate obtained under d) to provide wall-formation of microcapsules ;
and
f) adding a hardening agent as such as herein described in order to cross link the wall
formed around the hydrophobic core material
said process being characterized in that the positively charged high molecular weight
colloid is a type B gelatin, and typically has a molecular weight comprised between 40,000
and 100,000.
2. A process as claimed in claim 1, wherein the ratio between gelatin and the
negatively charged colloid is 3 : 2.
3. A process as claimed in claim 1, wherein the cooling step is carried out at a rate
comprised between 0.25 and 0.5°C/min.
4. A process as claimed in claim 1, wherein the hydrophobic core material is a flavor
ingredient or composition.
5. Microcapsules susceptible of being obtained by a process as claimed in claim 1.
6. Microcapsules as claimed in claim 5, comprising up to 80% by weight of
hydrophobic core material.
7. A food composition comprising, together with flavoring co-ingredients,
microcapsules as claimed in claim 5, as an active ingredient.
8. A method for improving the organoleptic properties of a flavoring composition,
which comprises adding to said composition, microcapsules as claimed in claim 5.
The invention relates to a complex coacervation process based on the use of type B gelatin as polycationic colloid,
for the preparation of "Halal" certified flavor-containing microcapsules.